The oils in coffee beans are part of what give coffee its flavor. If the beans you prefer are oilier, then freshness of the bean/grounds will really make a difference in the taste. So for those beans, keeping the beans sealed up and only grinding what you need when you need it will result in more flavor.

That said, grinding takes time and requires frequent cleaning of the grinder (in my experience). So it's a question of modest/moderate flavor improvement vs inconvenience.